Tinbergen's four questions

Tinbergen's four questions, named after Nikolaas Tinbergen, are complementary categories of explanations for behaviour. It suggests that an integrative understanding of behaviour must include both a proximate and ultimate (functional) analysis of behaviour, as well as an understanding of both phylogenetic/developmental history and the operation of current mechanisms.[1]

When asked about the purpose of sight in humans and animals, even elementary school children can answer that animals have vision to help them find food and avoid danger (adaptation). Biologists have three additional explanations: sight is caused by a particular series of evolutionary steps (phylogeny), the mechanics of the eye (causation), and even the process of an individual’s development (ontogeny). Although these answers may be very different, they are consistent with each other. This idea was formulated in the 1960s when Tinbergen delineated the four questions based on Aristotle's Four Causes.[2] This schema constitutes a basic framework of the overlapping behavioural fields of ethology & anthropology, behavioural ecology, sociobiology & evolutionary psychology, and comparative psychology. It was in fact Julian Huxley who identified the first three questions, Niko Tinbergen gave only the fourth question, but Julian Huxley's questions failed to distinguish between survival value and evolutionary history, so Tinbergen's fourth question helped resolve this problem.[3]

Darwin’s theory of evolution by natural selection is the only scientific explanation for why an animal’s behaviour is usually well adapted for survival and reproduction in its environment. However, claiming that a particular mechanism is well suited to the present environment is different from claiming that this mechanism was selected for in the past due to its history of being adaptive.[4] The literature conceptualizes the relationship between function and evolution in two ways. On the one hand, function and evolution are often presented as separate and distinct explanations of behaviour.[5] On the other hand, the common definition of adaptation, a central concept in evolution, is a trait that was functional to the reproductive success of the organism and that is thus now present due to being selected for; that is, function and evolution are inseparable. However a trait can have a current function that is adaptive without being an adaptation in this sense, if for instance the environment has changed. Imagine an environment in which having a small body suddenly conferred benefit on an organism when previously body size had had no effect on survival. A small body's function in the environment would then be adaptive, but it wouldn't become an adaptation until enough generations had passed to in which small bodies were advantageous to reproduction for small bodies to selected for. Given this, it is best to understand that presently functional traits might not all have been produced by natural selection.[6] The term “function” is preferable to “adaptation”, because adaptation is often construed as implying that it was selected for due to past function.

Evolution captures both the history of an organism via its phylogeny, and the history of natural selection working on function to produce adaptations.[7] There are several reasons why natural selection may fail to achieve optimal design (Mayr 2001:140–143; Buss et al. 1998). One entails random processes such as mutation and environmental events acting on small populations. Another entails the constraints resulting from early evolutionary development. Each organism harbors traits, both anatomical and behavioural, of previous phylogenetic stages, since many traits are retained as species evolve. Reconstructing the phylogeny of a species often makes it possible to understand the "uniqueness" of recent characteristics: Earlier phylogenetic stages and (pre-) conditions which persist often also determine the form of more modern characteristics. For instance, the vertebrateeye (including the human eye) has a blind spot, whereas octopus eyes do not. In those two lineages, the eye was originally constructed one way or the other. Once the vertebrate eye was constructed, there were no intermediate forms that were both adaptive and would have enabled it to evolve without a blind spot.

Hormones: Chemicals used to communicate among cells of an individual organism. Testosterone, for instance, stimulates aggressive behaviour in a number of species.

Pheromones: Chemicals used to communicate among members of the same species. Some species (e.g., dogs and some moths) use pheromones to attract mates.

In examining living organisms, biologists are confronted with diverse levels of complexity (e.g. chemical, physiological, psychological, social). They therefore investigate causal and functional relations within and between these levels. A biochemist might examine, for instance, the influence of social and ecological conditions on the release of certain neurotransmitters and hormones, and the effects of such releases on behaviour, e.g. stress during birth has a tocolytic (contraction-suppressing) effect. However, awareness of neurotransmitters and the structure of neurons is not by itself enough to understand higher levels of neuroanatomic structure or behaviour: "The whole is more than the sum of its parts." All levels must be considered as being equally important: cf. transdisciplinarity, Nicolai Hartmann's "Laws about the Levels of Complexity."

In the latter half of the twentieth century, social scientists debated whether human behaviour was the product of nature (genes) or nurture (environment in the developmental period, including culture). The consensus among biologists now is that behaviour is the product of gene-environment interaction, in which the whole can be more than the sum of the parts, that is, the genetic and environmental components. By way of contrast, tallness may simply be the sum of “tall genes” and an environment rich in food.

An example of interaction (as distinct from the sum of the components) involves familiarity from childhood. In a number of species, individuals prefer to associate with familiar individuals but prefer to mate with unfamiliar ones (Alcock 2001:85–89, Incest taboo, Incest). By inference, genes affecting living together interact with the environment differently from genes affecting mating behaviour. A homely example of interaction involves plants: Some plants grow toward the light (phototropism) and some away from gravity (gravitropism). Such species react to the same environment in different ways because of different genes.

A related concept is labeled “biased learning” (Alcock 2001:101–103) and “prepared learning” (Wilson, 1998:86–87). For instance, after eating food that subsequently made them sick, rats are predisposed to associate that food with smell, not sound (Alcock 2001:101–103). Many primate species learn to fear snakes with little experience (Wilson, 1998:86–87).[8]

The figure shows the causal relationships among the categories of explanations. The left-hand side represents the evolutionary explanations at the species level; the right-hand side represents the proximate explanations at the individual level. In the middle are those processes’ end products—genes (i.e., genome) and behaviour, both of which can be analyzed at both levels.

Evolution, which is determined by both function and phylogeny, results in the genes of a population. The genes of an individual interact with its developmental environment, resulting in mechanisms, such as a nervous system. A mechanism (which is also an end-product in its own right) interacts with the individual’s immediate environment, resulting in its behaviour. Here we return to the population level. Over many generations, the success of the species’ behaviour in its ancestral environment (or more technically, the environment of evolutionary adaptedness [EEA]) may result in evolution as measured by a change in its genes.

In sum, there are two processes—one at the population level and one at the individual level—which are influenced by environments in three time periods.

Four ways of explaining the Westermarck effect, the lack of sexual interest in one’s siblings (Wilson, 1998:189–196):

Function: To discourage inbreeding, which decreases the number of viable offspring.

Phylogeny: Found in a number of mammalian species, suggesting initial evolution tens of millions of years ago.

Causation: Little is known about the neuromechanism.

Development: Results from familiarity with another individual early in life, especially in the first 30 months for humans. The effect is manifested in nonrelatives raised together, for instance, in kibbutzs.

The four-question schema is used as the central organizing device in many animal behaviour, ethology, behavioural ecology and evolutionary psychology textbooks (e.g., Alcock, 2001) . One advantage of this organizational system, what might be called the "periodic table of life sciences," is that it highlights gaps in knowledge, analogous to the role played by the periodic table of elements in the early years of chemistry.

1. Causation

2. Ontogeny

3. Adaptation

4. Phylogeny

a. Molecule

b. Cell

c. Organ

d. Individual

e. Family

f. Group

g. Society

This "biopsychosocial" framework clarifies and classifies the associations between the various levels of the natural and social sciences, and it helps to integrate the social and natural sciences into a "tree of knowledge" (see also Nicolai Hartmann's "Laws about the Levels of Complexity"). Especially for the social sciences, this model helps to provide an integrative, foundational model for interdisciplinary collaboration, teaching and research (see The Four Central Questions of Biological Research Using Ethology as an Example -- PDF).

^”Phylogeny” often emphasizes the evolutionary genealogical relationships among species (Alcock 2001:492; Mayr, 2001:289) as distinct from the categories of explanations. Although the categories are more relevant in a conceptual discussion, the traditional term is retained here.

^”Biased learning” is not necessarily limited to the developmental period.